Power routing in a large digital integrated circuit (IC), such as a large “sea of gates”, is normally done by means of thick metal stripes (usually the two top layers in an IC creation process) from “north-to-south” and/or “west-to-east” over the entire digital area (“north-to-south” and “east-to-west” are used in this description to indicate a first direction and a second direction, respectively, which are essentially perpendicular to each other, and are thus not used to denote the normal geographical directions north-to-south and east-to-west, although they could coincide).
FIG. 1 shows an example of such power routing in the form of a power-supply distribution network 100. In one metal layer metalz, the current flows, for example, from north-to-south, in the other metal layer metalz+1 it flows from west-to-east. Just a small part is shown of the entire network which extends in all directions: north, south, west and east. By connecting both layers with each other by means of vias 130, a virtual mesh is created allowing the current to flow in many directions. As seen in FIG. 1, stripes 110, 120 and 110′, 120′ of ground and supply voltage are alternately routed in both metals layers metalz, metalz+1, respectively.
The present inventors have identified the following problems/drawbacks with a power routing of the type depicted in FIG. 1.
Firstly, it does not add decoupling capacitance to this two-layer power mesh directly. Therefore, in order to get stable digital circuitry, the power supply must be decoupled, which requires additional components.
Secondly, there is a risk of causing a relatively large amount of IR drop. As is well known per se, current through a wire causes a voltage drop, since a wire has a certain resistance, no matter how small. The voltage drop (Vdrop) can be calculated using the formula Vdrop=I*R, where I denotes the current and R denotes the resistance. Voltage drop in the power supply may introduce problems with the behavior of the circuitry being supplied by the power supply.
Thirdly, unwanted signals (EM noise, for instance) from the circuitry below or towards the circuitry below can pass through. Noise can cause delayed or false switching of the circuitry, resulting in unpredictable behavior. The supply voltage is normally routed in the top layer as well, which makes things even worse (since the supply voltage, or “POWER”, is in many cases the aggressor).
Therefore, there is a need for improvements with respect to these problems.